Method for operating a drive system, and drive system

ABSTRACT

In a method for operating a drive system, and drive system, having a rectifier and at least one inverter including an electric motor, the electric motor is connected at the AC-voltage-side connection of the inverter, the DC-voltage-side connection of the inverter is connected via inductance(s) in addition to the line inductance, to the DC-voltage-side connection of the rectifier, a capacitance is connected at the DC-voltage-side connection of the inverter and/or at the DC-voltage-side connection of the rectifier, a series circuit, including a resistor and a controllable semiconductor switch is connected at the DC-voltage-side connection of the inverter and/or at the DC-voltage-side connection of the rectifier, the braking chopper being operated using a single frequency during the particular time span in which the braking chopper is in operation, the frequency, e.g., being set apart from the resonant frequency of the resonant circuit including the inductance or the capacitances.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 17/250,523, which is the national stage of PCT/EP2019/025239,having an international filing date of Jul. 19, 2019, and claimspriority to Application No. 102018005932.5, filed in the FederalRepublic of Germany on Jul. 30, 2018, each of which is expresslyincorporated herein in its entirety by reference thereto.

FIELD OF THE INVENTION

The present invention relates to a method for operating a drive systemand to a drive system.

BACKGROUND INFORMATION

Certain conventional electric motors can be operated as a generator or amotor, and the voltage at the DC-voltage-side connection of an invertersupplying the electric motor rises in a generator-mode operation if acapacitor is connected at this connection.

SUMMARY

Example embodiments of the present invention provide a drive system thatcan be operated in a safe manner.

According to example embodiments of the present invention, in a methodfor operating a drive system having a rectifier and at least oneinverter with an electric motor, the electric motor is connected at theAC-voltage-side connection of the inverter, the DC-voltage-sideconnection of the inverter is connected to the DC-voltage-sideconnection of the rectifier via at least one inductance in addition tothe line inductance, a capacitance, in particular, a non-polarcapacitor, in particular, a film capacitor, is connected at theDC-voltage-side connection of the inverter and/or at the DC-voltage-sideconnection of the rectifier, a series circuit, that includes a resistorand a controllable semiconductor switch, i.e., a braking chopper, isconnected at the DC-voltage-side connection of the inverter and/or atthe DC-voltage-side connection of the rectifier, and the braking chopperis operated using a single frequency f during the particular time spanin which the braking chopper is in operation, the frequency, inparticular, being spaced apart from the resonant frequency of theresonant circuit including the inductances and the capacitance orcapacitances.

This has the advantage that the frequency is able to be spaced apartfrom a resonant frequency of the drive system. The excitation ofoscillations is therefore avoidable and the drive system mayconsequently be operated in a safe manner, in particular, in terms ofthe voltage. This is considered advantageous, in particular, whenmultiple inverters are jointly supplied from a DC-voltage circuit, inparticular, an intermediate circuit. Of importance in this context isthe interaction of the inductances with the capacitance(s) for forming asystem that has a resonant frequency.

According to example embodiments, the voltage supplying the seriesconnection, and thus the intermediate circuit voltage, i.e., inparticular, the voltage applied at the DC-voltage-side connection of theinverter, is acquired. This offers the advantage that the operation ofthe braking chopper is able to be carried out in a voltage-dependentmanner. The actuating signal for the braking chopper may thus begenerated by a control electronics, the actuating signal being able tobe generated as a function of the intermediate-circuit voltage on theone hand and as a function of a controllable time basis on the otherhand.

According to example embodiments, the acquired value of the voltage,i.e., the intermediate circuit voltage, is digitized and conveyed as adigital serial data stream to a first digital filter, in particular, anFIR filter, on the one hand, and to a second digital filter, inparticular, an FIR filter, on the other hand, the second digital filterbeing started at a time offset from the first digital filter, the timeoffset, in particular, amounting to one half of the filter length. Thisoffers the advantage that the dead time can be reduced in that thedigital data stream is able to be evaluated at a more rapid repeat rate.

According to example embodiments, the output signals of both filters areconveyed to a comparison device for a comparison with the first and thesecond threshold value in each case, the output signals of thecomparison device being logically linked with a signal generated by acontrollable time basis, in particular, by a controllable clockgenerator, for the generation of an actuating signal for the brakingchopper. This has the advantage that a voltage-dependent condition isable to be linked with a time-dependent condition. The actuating signalfor the braking chopper is therefore able to be generated such that thebraking chopper can be operated using a fixed frequency, in particular,a single fixed frequency, whenever the intermediate circuit voltage liesin the value range provided for this purpose. The compliance with thetime-dependent condition ensures that the braking chopper is activatedat the clock pulse of the frequency and that the braking chopper isdeactivated at the clock pulse of the frequency. However, the operationis always conducted subject to the caveat that the voltage lies in theprovided range since the braking chopper will otherwise remain switchedoff.

According to example embodiments, the braking chopper is deactivatedwhenever the intermediate circuit voltage drops below a threshold valueU2. This is considered advantageous insofar as the intermediate circuitvoltage does not drop to an unintentionally low value on account of thebraking chopper.

According to example embodiments, the braking chopper is activated whenthe intermediate circuit voltage exceeds a first threshold value U1, inparticular, and when either no activation has had previously takenplace, or the most recent activation to have previously taken place wasearlier by more than a predefined time period T, time period T beingequal to the multiplicative inverse of frequency f. This has theadvantage that the braking chopper may be activated after U1 has beenexceeded, but only if the braking chopper is activated for the firsttime or is reactivated for time-related reasons after an interruption ofits operation. However, the interruption must have lasted longer thanthe multiplicative inverse of the frequency and the intermediate circuitvoltage must be greater than threshold value U2.

According to example embodiments, first switching threshold U1 isgreater than second switching threshold U2. This has the advantage thatU1 functions as an activation threshold, and U2 functions as adeactivation threshold.

According to example embodiments, following the activation of thebraking chopper, a deactivation of the braking chopper is carried outafter, especially no later than, a time period whose value is equal to aproduct (q×T) of a time period T and a factor q, the factor q having avalue of between zero and one, in particular, a value from the range of0.8 to 0.98.

This corresponds to the maximal duration of the activation of thebraking chopper within period T. The result is a forced deactivation.This similarly also applies in the reverse case so that the forcedactivation if previously maximally deactivated.

This offers the advantage that in order to maintain the frequency, thedeactivation is forced even when the intermediate circuit voltage isactually so high that the intermediate circuit voltage should belowered, i.e., energy of the intermediate circuit should be convertedinto heat via the braking chopper and the resistor switched in seriesand functioning as brake resistor. It is therefore actuallydisadvantageous to require the braking chopper to adhere to thefrequency, but it prevents the excitation of resonant oscillations. Thebraking chopper is operable, e.g., at the actuation limit. It is thenactivated for maximally 0.98×T and deactivated 0.02×T instead of apermanent activation. This loss in actuating reserves is taken intoaccount during the configuration of the brake resistor and does notconstitute a disadvantage.

According to example embodiments, the multiplicative inverse of timeperiod T is greater than the resonant frequency of the resonant circuitincluding the inductances and the capacitance or capacitances. Thisoffers the advantage that the frequency is able to be spaced apart fromthe resonant frequency, in particular, by more than 40% of the value ofthe resonant frequency.

According to example embodiments, if the activation threshold U1 hadbeen exceeded or reached at least once in the past and intermediatecircuit voltage U_ZK lies above U2, the braking chopper is deactivatedif the time interval from the previously undertaken deactivation reachesa time interval whose value is equal to a product (p×T) of a time periodT and a factor p, factor p having a value of between zero and one, inparticular, a value in the range from 0.8 to 0.98.

This has the advantage that the braking chopper is deactivated in atimely manner so that the frequency is still maintained.

According to example embodiments, if activation threshold U1 had beenexceeded or reached at least once in the past and the intermediatecircuit voltage U_ZK lies above U2, the braking chopper is activated ifthe time interval from the previously undertaken deactivation reaches atime interval whose value is equal to a product (q×T) of a time period Tand a factor q, the factor q having a value of between zero and one, inparticular, a value from the range of 0.8 to 0.98. This offers theadvantage that the braking chopper is activated in a timely manner sothat the frequency is still maintained.

According to example embodiments, factor q is equal to factor p. Thisoffers the advantage that the activation frequency and the deactivationfrequency are similar and therefore no additional excitation of beatfrequencies and their harmonics takes place.

According to example embodiments, the acquired value of the voltage,i.e., the intermediate circuit voltage, is acquired, digitized, andconveyed as a digital serial data stream to a first digital filter, inparticular, an FIR filter, on the one hand, and to a second digitalfilter, in particular, an FIR filter on the other hand, the seconddigital filter being started at a time offset from the first digitalfilter, the time offset, in particular, amounting to one half of afilter length. This offers the advantage that the exceeding orundershooting of the threshold values is able to be detected morerapidly.

According to example embodiments, the output signals of both filters areconveyed to a comparison device for a comparison with the first and thesecond threshold value, the output signals of the comparison devicebeing logically linked with a signal generated by a controllable timebasis, in particular, by a controllable clock generator, for thegeneration of an actuating signal for the braking chopper. This has theadvantage that the voltage-dependent condition is linkable with atime-dependent condition.

According to example embodiment of the present invention, in a drivesystem for carrying out a previously mentioned method, the additionalinductance is at least ten times, in particular, at least one hundredtimes, greater than the line inductance. This is considered advantageousinsofar as the resonant frequency is substantially independent of theline inductance. In this manner, the additional inductance may bedimensioned so that the resonant frequency lies in a predefined valuerange, and the frequency for operating the braking chopper has asufficient clearance from this resonant frequency.

Further features and aspects of example embodiments of the presentinvention are described in greater detail below with reference to theappended schematic Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates the structure of an inverter includinga braking chopper.

FIG. 2 schematically illustrates a drive system according to an exampleembodiment of the present invention.

FIG. 3 schematically illustrates the generation of signals as a functionof the intermediate circuit voltage.

FIG. 4 schematically illustrates the generation of the actuating signal,carried out as a function of the signals, for the braking chopper.

FIG. 5 schematically illustrates the oscillating circuit which—in theabsence of additional intermediate circuit inductances L—is formed fromthe line inductance and intermediate-circuit-side capacitances C_ZK.

DETAILED DESCRIPTION

As schematically illustrated in FIG. 1 , an inverter has a rectifier 1,which may also be arranged as a regenerative rectifier. On theDC-voltage side, a capacitance C is provided at rectifier 1 which,however, is implemented only as a non-polar capacitor, in particular, asa film capacitor.

The voltage applied at capacitor C is acquired and conveyed to a signalelectronics 1, which generates the actuating signals for thecontrollable semiconductor switches disposed in the form of halfbridges.

Fed from the AC-voltage-side connection of the inverter is an electricmotor M, in particular, a three-phase motor.

The voltage applied at capacitor C is conveyed to the DC-voltage-sideconnection of the inverter.

To protect against excess voltages at capacitor C, that is to say, toprotect against an excess intermediate circuit voltage, a series circuitthat includes a brake resistor R and a controllable semiconductor switch4 is provided, free-wheeling diodes also being provided.

The use of such a braking chopper therefore makes it possible to convertenergy from the intermediate circuit into heat with the aid of the brakeresistor, i.e., a brake resistor substantially arranged as an Ohmicresistor. In this manner, excess, system-critical voltage values areavoidable.

The actuating signal for semiconductor switch 4 is generated by signalelectronics 2, to which the acquired intermediate circuit voltage valuesare conveyed as well.

Rectifier 1 is connected via its AC-voltage-side connection to theAC-voltage supply network.

Rectifier 1 is also implementable as a regenerative AC/DC converter.

As illustrated in FIG. 2 , multiple inverters are able to be connectedto the intermediate circuit via additional inductances L, so that energyis withdrawn from the intermediate circuit during the motoric operationof the electric motor, in particular, the three-phase motor, fed by therespective inverter 20, and energy is supplied in the generator-modeoperation.

A braking chopper including brake resistor R is also allocated to eachinverter 20.

Capacitance C_ZK may be arranged as a non-polar capacitor, inparticular, as a film capacitor.

However, only a single brake resistor has to be connected to an inverterfor the safe operation of the drive system including multiple inverters.The braking choppers of the other inverters may remain open.

As an alternative, a capacitance C_ZK is connected in each inverter 20at its respective DC-voltage-side connection, to which a series circuitincluding a respective controllable semiconductor switch, in particular,a braking chopper, and a resistor, in particular, a brake resistor, areswitched in parallel. On the one hand, the upper potential of theDC-voltage-side connection of inverter 20 is connected via an inductanceL to the upper potential of intermediate circuit voltage U_ZK. On theother hand, the lower potential of the DC-voltage-side connection ofinverter 20 is connected via an inductance L to the lower potential ofintermediate circuit voltage U_ZK.

The intermediate circuit voltage in turn is generated using anetwork-supplied rectifier 21 at whose DC-voltage-side connection anon-polar capacitor is situated.

As illustrated in FIG. 5 , capacitances C_ZK of the inverters would thusbe connected via line inductance L_ZK if the additional inductances werenot available. Inverters 20 would therefore introduce into the drivesystem excitations 50 which excite oscillations of the oscillatingcircuit that includes capacitances C_ZK and line inductance L.

However, since inductances L illustrated in FIG. 2 are provided inaddition, which are at least ten times greater than the line inductancesL_ZK of the intermediate circuit, the resonant frequency is thus able tobe accurately brought to an intended value range, e.g., 2 kHz, with adeviation of less than 10%.

According to example embodiments of the present invention, the brakingchopper is operated at a frequency of 3 kHz, in particular, at a systemvoltage of 400V to 500V, so that the braking chopper is unable to exciteany oscillation of the resonant circuit. Since the pulse-widthmodulation frequencies of the controllable semiconductor switches of theinverters are also operated at a frequency above the value range, forexample, at 4 kHz, 8 kHz, or 16 kHz, these inverters are likewise unableto excite an oscillation of the resonant circuit.

At a lower system voltage such as 200 Volt to 240 Volt, it is alsopossible to select 5 kHz as the frequency, for example.

The operating method and operating conditions of the braking chopper aredescribed in greater detail with reference to FIGS. 3 and 4 , FIG. 3schematically illustrating the voltage-dependent conditions, and FIG. 4schematically illustrating the time-dependent conditions for theactuation of the braking chopper.

As illustrated in FIG. 3 , the acquired intermediate circuit voltage,which is converted into a serial digital data stream with the aid of adelta-sigma converter, is conveyed to two digital filters 31, inparticular, FIR filters, whose respective start signals are mutuallyoffset in time by one half of a filter length Ta/2. The start signalsare generated by a time basis 30 to which a synchronization signal istransmitted.

The digital filters 31 are arranged as a digital low-pass filter, thatis to say, in particular, with a damping power that has a window-typedependency on the frequency.

The output signal of filters 31 is conveyed to a respectiveserial-parallel converter 32, whose digital parallel output signal isforwarded to a respective comparator 33 in each case, which compares theoutput signal, i.e., the acquired respective voltage value, to a firstthreshold value U1 and to a second voltage value U2.

First threshold value U1 corresponds to a minimally required voltage forinducing an activation if the braking chopper had previously beendeactivated. Second threshold value U2 marks a voltage which, ifundershot, always causes the braking chopper to be deactivated.

The result of the comparison with first threshold value U1 is output ona signal line 37.

The result of the comparison with second threshold value U2 is output ona second signal line 38, which is routed to a linking device 39.

In a voltage monitoring device 34, it is checked whether first thresholdvalue U1 is greater than zero, and if this is not the case, adeactivation of the drive system is initiated when negative voltages aredetected, or the drive system is brought to a safe state.

To this end, first signal line 37 leads from respective comparator 33 toa respective AND-conjunction 35 with the respective result of themonitoring of first threshold value U1, i.e., with the output signal ofthe voltage monitoring device 34 for the deactivation upon the detectionof negative voltages.

Comparator 33 is configured to take a hysteresis into account in therespective comparison.

Linkage device 39 links the two signals on both signal lines 38 to a2-bit item of information, which is forwarded as BRC_Info. In theprocess, the item of information is therefore encoded as to whether bothsignals are zero or whether at least one of the two signals is unequalto zero or whether both signals are unequal to zero. Thus, it is encodedwhether the intermediate circuit voltage is greater than the activationthreshold, is lower than the deactivation threshold, or lies between thetwo threshold values.

The output signals of the AND-conjunctions 35 are conveyed to signalgeneration device 36, just like the output signal of linkage device 39.This signal generation device 36 thus supplies the aforementioned signalBRC_Info and a signal Ein_U-puls, which is set when threshold value U1is exceeded and is reset when it is undershot.

Because of the dual voltage processing at a time offset of one half of afilter time according to FIG. 3 , a more rapid detection of theexceeding or of an undershooting of the threshold values (U1, U2) ispossible.

As illustrated in FIG. 4 , signal BRC_Info is forwarded to a time basis41, whose output signals are conveyed to linkage devices 42 and 43,whose output signals are conveyed to a signal generation device 44.

As illustrated in FIGS. 3 and 4 , a time condition and a voltagecondition are thereby taken into account in the generation of actuatingsignal BRC for the braking chopper.

On the one hand, the braking chopper is activated when the voltage liesabove threshold value U1 and is deactivated when it lies below thresholdvalue U2.

U2 is smaller than U1.

Thus, when intermediate circuit U_ZK increases from zero, the brakingchopper is activated only when U1 is exceeded. As soon as U2 isundershot, the braking chopper is always deactivated. After theactivation of the braking chopper, a deactivation of the braking choppertakes place after a time period q×T at the latest. Time period T is themultiplicative inverse of the frequency specified for the brakingchopper, e.g., 3 kHz, for example. The factor q has a value of betweenzero and one and is selected, for example, to be large. For example, itamounts to 0.95.

In addition, if activation threshold U1 had been reached at least oncein the past and the intermediate circuit voltage U_ZK still lies aboveU2, the braking chopper is deactivated when time period T is reachedthat has elapsed since the previously implemented deactivation, and thebraking chopper is activated when time period T since the previouslyexecuted activation has elapsed.

An effect of these voltage conditions and time conditions is that thebraking chopper is always operated at the frequency f=1/T when it is inoperation. It remains deactivated in the other case.

In this manner, no undesired oscillation is therefore excitable in theintermediate circuit by the operation of the braking chopper.

Even if—purely theoretically—different frequencies have non-vanishingamplitudes in the Fourier analysis of the time characteristic due to thefinite operating period of the braking chopper, the energy introductionin the resonant frequency is too low to excite a dangerous or undesiredoscillation.

A robust operation of the drive system with multiple inverters jointlysupplied with a DC-voltage, and the avoidance of resonant oscillationsand resonance increases are able to be obtained. In addition, areduction of the loading of the components is able to be brought aboutbecause the AC-voltage component of the intermediate circuit current isreduced. In addition, no information about the actual intermediatecircuit capacitance of the system is required. As a result, no controlneeds to be parameterized individually. Even a plug & play configurationis possible in this manner. Moreover, it is possible that inverters areretroactively able to be connected as well without requiring areparameterization of the system. The hysteresis of the braking chopperautomatically and correctly adjusts itself through the describedcontrol. However, the connection point of the brake resistor may also beimplemented at different positions for this purpose.

LIST OF REFERENCE CHARACTERS

-   1 rectifier-   2 signal electronics-   3 inverter-   4 controllable switch, in particular braking chopper-   5 converter-   20 inverter-   21 rectifier-   30 time basis-   31 filter, in particular digital filter-   32 serial-parallel converter-   33 comparator with hysteresis-   34 voltage monitoring for deactivation upon the detection of    negative voltages-   35 AND-conjunction-   36 signal generation-   37 first signal line-   38 second signal line-   39 linking device-   40 voltage-dependent logic-   41 controllable time basis, in particular controllable counter-   42 linking device-   43 linking device-   44 signal generation device-   50 excitation-   Clk clock signal-   BRC actuating signal for controllable semiconductor switch, in    particular braking chopper-   BRC_Info input signal for time basis 41-   Ein_U_puls activation signal-   Aus_U_puls deactivation signal-   Sync synchronization signal-   Load load signal-   Koeff coefficient-   Data Clock clock signal-   U1 activation threshold-   U2 deactivation threshold-   R brake resistor-   M electric motor-   C capacitor-   L inductance-   L_ZK line inductance-   C_ZK intermediate circuit-side capacitance of the respective    inverter

What is claimed is:
 1. A drive system, comprising: a rectifier includinga DC-voltage-side connection; an inverter including an AC-voltage-sideconnection and a DC-voltage-side connection, the DC-voltage-sideconnection of the inverted connected to the DC-voltage-side connectionof the rectifier via an inductance and a line inductance; an electricmotor connected to the AC-voltage-side connection of the inverter; acapacitance connected to the DC-voltage-side connection of the inverterand/or at the DC-voltage-side connection of the rectifier; and a seriescircuit, arranged as a braking chopper, that includes a resistor and acontrollable semiconductor switch, connected to the DC-voltage-sideconnection of the inverter and/or at the DC-voltage-side connection ofthe rectifier; and wherein the braking chopper is adapted to operateusing a single frequency during a particular time span in which thebraking chopper is operated, the single frequency being offset from aresonant frequency of a resonant circuit that includes the inductancesand the capacitance.
 2. The drive system according to claim 1, whereinthe capacitance includes a non-polar capacitor and/or a film capacitor.3. The drive system according to claim 1, further comprising a firstdigital filter and a second digital filter adapted to receive anacquired voltage value of a voltage supplying the series circuit and/ora voltage applied at the DC-voltage-side connection of the inverter, thesecond digital filter adapted to start at a time offset from the firstdigital filter.
 4. The drive system according to claim 3, wherein thefirst digital filter and/or the second digital filter includes an FIRfilter.
 5. The drive system according to claim 3, wherein the timeoffset corresponds to one half of a filter length.
 6. The drive systemaccording to claim 3, further comprising a comparison device adapted tocompare output signals of the first digital filter and the seconddigital filter with first and second threshold values, output signals ofthe comparison device being logically linked with a signal generated bya controllable time basis to generate an actuating signal for thebraking chopper.
 7. The drive system according to claim 6, wherein thecontrollable time basis includes a controllable clock generator.
 8. Thedrive system according to claim 1, wherein the braking chopper isadapted to be deactivated in response to an intermediate circuit voltagedropping below a second threshold value, the intermediate circuitvoltage being represented by a voltage that supplies the series circuit.9. The drive system according to claim 1, wherein the braking chopper isadapted to be activated in response to the intermediate circuit voltageexceeding a first threshold value, the intermediate circuit voltagebeing represented by a voltage that supplies the series circuit.
 10. Thedrive system according to claim 1, wherein the braking chopper isadapted to be activated in response to an intermediate circuit voltageexceeding a first threshold value and in response to either noactivation having had previously taken place or a most recent activationhaving previously taken place is earlier by more than a predefined timeperiod that is equal to a multiplicative inverse of the singlefrequency, the intermediate circuit voltage being represented by avoltage that supplies the series circuit.
 11. The drive system accordingto claim 8, wherein the braking chopper is adapted to be activated inresponse to the intermediate circuit voltage exceeding a first thresholdvalue, first threshold value being greater than the second thresholdvalue.
 12. The drive system according to claim 1, wherein the brakingchopper is adapted to be deactivated, following an activation of thebraking chopper, after and/or no later than a time period having a valuethat is equal to a product of a time period and a factor, the factorhaving a value of between zero and one.
 13. The drive system accordingto claim 12, wherein the factor has a value of between 0.8 and 0.98. 14.The drive system according to claim 12, wherein a multiplicative inverseof the time period is greater than the resonant frequency of theresonant circuit.
 15. The drive system according to claim 11, whereinthe braking chopper is adapted to be deactivated, if the first thresholdis exceeded or reached at least once and an intermediate circuit voltageis above the second threshold value, in response to a time interval froma previously undertaken deactivation reaching a time interval whosevalue is equal to a product of a time period and a factor, the factorhaving a value of between zero and one.
 16. The drive system accordingto claim 15, wherein the factor has a value of between 0.8 and 0.98. 17.The drive system according to claim 11, wherein the braking chopper isadapted to be activated, if the first threshold value is exceeded orreached at least once and an intermediate circuit value is above thesecond threshold value, in response to a time interval from a previouslyundertaken activation reaching a time interval whose value is equal to aproduct of a time period and a factor, the factor having a value ofbetween zero and one.
 18. The drive system according to claim 17,wherein the factor has a value of between 0.8 and 0.98.
 19. The drivesystem according to claim 11, wherein the braking chopper is adapted tobe deactivated, if the first threshold value is exceeded or reached atleast once and an intermediate circuit voltage is above the secondthreshold value, in response to a time interval from a previouslyundertaken deactivation reaching a time interval whose value is equal toa product of a time period and a first factor, the first factor having avalue of between zero and one; wherein, the braking chopper is adaptedto be activated, if the first threshold value is exceeded or reached atleast once and an intermediate circuit voltage is above the secondthreshold value, in response to a time interval from a previouslyundertaken activation reaching a time interval whose value is equal to aproduct of a time period and a second factor, the second factor having avalue of between zero and one; and wherein the first factor equals thesecond factor.
 20. The drive system according to claim 1, wherein theinductance is at least ten times greater than the line inductance. 21.The drive system according to claim 1, wherein the inductance is atleast one hundred times greater than the line inductance.